Pulse delay communication system



Feb. 12, 1952 E. M. DELORAINE PULSE DELAY COMMUNICATION SYSTEM 12Sheets-Sheet 1 Original Filed Nov. 14, 1945 COMMON EQUIPMENT TO OTHERLINKS SECOND LINK CIRCUIT FIRST LINK CIRCUIT E .W MM T O N L E D m M D NU M D, E

A TTOPNEI Feb. 12, 1952 M, DELQRAINE 2,584,987

PULSE DELAY COMMUNICATION SYSTEM Original Filed Nov. 14, 1945 12Sheets-Sheet 2 MASTER FREQUENCY DIVIDER *O$CJLLN [0 KC FIG. 4

Fl T R INVENTOR. EDMUND M. DELORAINE ATTORNEY Feb. 12, 1952 E. M.DELORAINE PULSE DELAY COMMUNICATION SYSTEM 12 Sheets-Sheet 5 OriginalFiled Nov. 14, 1945 IN V EN TOR.

EDMUND M. DELORAINE A 7'7'ORNEV Feb. 12, 1952 E. M. DELORAINE PULSEDELAY COMMUNICATION SYSTEM 12 Sheets-Sheet 5 70 CONNECT/ON 3 5+ N0 1 leCONNECT/M v vv will R T R CIRCUIT I r IF 1 P v I30 i 12! |22 1: 5+ /-I4OB I25 I26 j Y 1 TL SECOND REGISTER CIRCUIT THIRD REGISTER CIRCUIT HFOURTH H REGISTERF CIRCUIT I37 Fl FTH I38 REGISTER CIRCUIT L Has FIG 7INVENTOR. EDMUND M. DELORAINE Feb. 12, 1952 E. M. DELORAINE PULSE DELAYCOMMUNICATION SYSTEM 12 Sheets-Sheet 6 Original Filed Nov. 14, 1945 lI491 SECOND I DELAY I GATE 1 x510 ZEE EAT E 7 w 6 3 L 7 3 IL THIRD DELAYGATE I44 THIRD ZERO GATE FOURTH 5 ZERO GATE 20 MS DELAY 40 MS DELAY MSDELAY FOURTH [5| DELAY GATE FIFTH IDELAY GATE FIFTH INVENTOR.

EDMUND M. DELORAINE FIG. 8

ATTORNEY 1952 E. M. DELORAINE PULSE DELAY COMMUNICATION SYSTEM OriginalFiled Nov. 14, 1945 12 Sheets-Sheet 7 FIG IO FIG.

IOD

INVENTOR. EDMUND M. DELORAIN E ATTORNEY E. M. DELORAINE PULSE DELAYCOMMUNICATION SYSTEM Feb. 12, 1952 12 Sheets-Sheet 8 Original Filed Nov.14, 1945 FIG. I2

4 INVENTOR. EDMUND M. DELORAINE M A TOPNEV Feb. 12, 1952 E. M. DELORAINEPULSE DELAY COMMUNICATION SYSTEM Original Filed Nov. 14, 1945 FIG. l3

12 Sheets-Sheet 9 PHASE CORRECTOR LOCK-lair! 05G FREQ. DIVIDER 200 KC.T0SOKC CLIPPER & DIFFERENTIAT- lNG CIRCUIT SYNCHRONIIZED MULTl-Vl BRATORto KC IN V EN TOR.

EDMUND M. DELORAIN E ATTORNEY Feb. 12,-' 1952 E. M. DELORAINE 2,584,987

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EDMUND M. DELORAINE ATTORNEY 12 Sheets-Sheet 11 E. M. DELORAINE PULSEDELAY COMMUNICATION SYSTEM Feb. 12, 1952 Original Filed NOV. 14, 1945 INVEN TOR. EDMUND M.DELORAINE PRELIMINARY REGISTER SECOND REGISTER LASTREGISTER ATTORNEY Feb.

Original Filed Nov. 14, 1945 12 Sheets-Sheet 12 I I I I I I 224 I I I rI; 3 I PULSE I SHAPING L I AMPLIFI R I E 6 FI F" I 29 I PULSE z I I IIER Z27 1 I as I I I I I 22a 5+ 4 I I I I GAIN I j I I I CONTRO I I laaI I I HI I T VI I ow PAss FILTER & I I AUDIO AMPLIFI I I I FIRST if j5+ I 229 I I 1/ I I I I I 233 J- h 1 I L I I '1 I I I T I 232 I 222 I y5' I 1 SECONDI l 5..

COUNTER I B- LAST' COUNTEE I I I I I I I IN V EN TOR.

EDMUND M. DELORAINE Patented Feb. 12, 1952 res TENT OFFICE PULSE DELAYCQMMUNICATION SYSTEM Continuation of application Serial No. 628,613,November 14, 1945. This application May 13, 1950, Serial No. 161,831

56 Claims. i

This application is a continuation of my copending application, SerialNo. 628,613, filed November 14, 1945, now abandoned.

This invention relates to communication systems and more particularly toexchange systems for use in telephony.

In telephone systems generally in use, interconnection betweensubscribers lines through the various trunking lines in telephoneexchange requires considerable mechanical switching and a large plantset up. Furthermore, large numbers of interconnecting lines aregenerally required in the exchange so that connection may be madebetween any two lines incoming into the system. Likewise, considerablecomplication is presented in the signalling system for line selectionsand ringing.

Some replacement of mechanical switching systems by electronic switcheshave been proposed but, in general, all of these systems require stillthe mechanical selection of lines for interconnection. The electronicswitches as proposed generally are used simply to replace some of themechanical switches in the system. Furthermore, ringing and othersignalling is carried through conventional switching circuits in thesame manner as in the telephone systems generally in use.

It is an object of my invention to provide a switching circuit forinterconnection of channels wherein substantially all the signalling aswell as the communication may be carried through electronic switchingmeans.

It is a further object of my invention to provide a switching system forinterconnecting any two channels of a plurality of channels for transferof communication in which each of the channels is given a predeterminedtime spacing and interconnection is effected by effectively delaying theindication signals a predetermined amount equal to substantially thedifierence in time position assigned to the channels to beinterconnected.

It is a still further object of my invention to provide an exchangesystem in which each of a plurality of channels is connected to a commondistributor unit which serves successively to scan the lines so thateach has a predetermined time position in the scanning cycle and toproduce in response to signals of any one channel a time displacementequal substantially to the time displacement between the channels to beinterconnected so that the signals may be properly redistributed to thisoutput channel.

It is still a further object of my invention to provide an exchangesystem in which each of a plurality of lines for transferringcommunication signals is allotted a predetermined position in adistributor scanning cycle so that signals from all the lines inoperation are reproduced in parallel, for example in time displacedrelation, on a common interconnecting medium and in which thesecommunication signals are delayed a proper amount so that uponreapplication to the distributor system they will be applied to aselected other one of the lines of the system.

In a system according to my invention, a number of communicationchannels, dependent upon the number of trunking selectors provided inthe system, can be interconnected for simultaneous conversations.Furthemore, the system is extremely simple so far as equipment isconcerned and permits the construction of telephone exchanges withouttremendous outlays of equipment. Furthermore, in such a system it is notessential that a large central exchange be maintained but individualsmaller exchanges may be installed in diiierent centers of population asrequired, the whole system then being capable of interconnection tocover a large area.

In accordance with a feature of my invention,

. the signal or speech currents in the various lines displaced in timein accordance with the distributor time position. This distribution maybe readily accomplished by means of a cathode ray tube serving as adistributor which will sequentially scan the lines connected topredetermined terminals and respond if there is a signalling voltage onthe line. The channels may be separated by time selection and may beapplied through time displacement means and a low-pass filter whichserves to reproduce the audio envelope to the same or anotherdistributor also coupled to the lines. The incoming signals may serve toadjust the time displacement means so that they will represent the timediiierence between the time position of the calling line and theselected called line. The time displacement means may be an actual delayline of some form or an equivalent circuit which, while not producing anactual delay of the signals, will eflectively serve .to store the energyand release it after a predetermined interval equal to the desireddelay. In this manner, the interconnection of any one line with anyother line of the system may be accom plished. Upon makingthis'interconnection, the communication signals may pass through thesame delay means between the interconnected lines. Furthermore, sincethe scanning cycle covers each of the lines connected to thedistributor, as many simultaneous connections may be made as there aretime displacement trunking channels within the exchange.

Preferably, means are provided responsive to the interconnection of thelines to tie up these lines so that they cannot be selected by anothersubscriber attempting to get the connection. If

desired, any conventional type of busy signal may be applied to thesubscribers line when this condition exists so that he will know that hemust wait an interval for the line to become free so that he can makethe desired connection.

While I have broadly outlined certain objects and features of myinvention a better understanding of my invention and the objects andfeatures thereof may be had from the particular description of anembodiment and certain modifications thereof made with reference to theaccompanying drawings, in which:

Fig. 1 is a block diagram illustrating the general circuit set up;

Figs. 2 and 3 are sectional circuit diagrams and views respectively, ofa distributor tube used in my system;

Figs. 4 to 8 inclusive, constitute a circuit diagram of a link exchangein accordance with my invention;

Fig. 4. illustrating the common equipment.

Fig. 5 showing the pulse forming equipment.

Fig. 6 the line finder equipment.

Fig. '7 the dial register equipment, and

Fig. 8 the line selecting equipment;

Fig. 9 is a diagram illustrating how Figs. 4 to 8 inclusive, should bearranged to illustrate the complete circuit;

Fig. 10 is a set of curves used in explaining the operation of certainparts of the system;

Fig. 11 is a diagram in section of a delay line suitable for use in theequipment shown in Fig. 8;

Fig. 12 is an alternative form of circuit including both a commonequipment and a line finder circuit which may be substituted as a wholefor Figs. and 6 in accordance with my invention;

Fig. 13 is an alternative type of line finder circuit which may besubstituted for the circuit of Fig. 6 in accordance with my invention;

Fig. 1 is an alternative form of pulse forming circuit which may besubstituted for the circuit of Fig. 5;

Figs. 15 and 16 are respectively, alternative forms of dial register andline selecting circuits which may be substituted as a whole for the twocircuits of Figs. 7 and 8; and

Fig. 17 is a diagram illustrating how Figs. 4, 12, 14, 15 and 16 shouldbe arranged to illustrate the preferred alternative combinations ofcircuits of my invention.

In an example of my system as outlined above, the system may be dividedinto three parts as shown in Fig. 1; first, all the subscribers lines,twenty for example, assigned numerals 1 to 20, each of these lineshaving a subscriber subset equipment such as 2!; second, the equipmentcommon to all line circuits, hereafter referred to as common equipment22; and third, a group of link circuits one of which is needed fo eachsimultaneous call. Each of the link circuits may be further sub-dividedinto line finder circuit 23, dial pulse forming circuit 24, dialregister circuit 25 and line selecting circuit 26. These several majorcomponents are interconnected by wires 21-38 mon equipment 22. Thisequipment 22 performs a scanning function, preferably by means of asuitable tube having an electronic beam which sweeps each of the linesin turn.

When one of these lines has a potential indicative of a callingcondition, the common equipment 22 applies signals over wires 2'! andZfito all the link circuits in parallel and specifically to the linefinder circuit 23 of the first link (chosen for discussion). This linefinder 23 operates to find the calling line and transfer the signalsover wire 33 to the dial pulse forming circuit 24.

When dialing ensues, this circuit 24 produces dial pulses which arecounted and stored in dial register circuit 25. The dial pulse register25 then serves to control the line selector circuit 26 which maycomprise a delay line or other time displacement apparatus.

The incoming speech signals are then transferred from common equipment22 over wire 28, line finder circuit 23, wire 33, line selector circuit26 and thence over wire 36 back to the common equipment 22 from whencethey are applied to the selected outgoing line. The part of Fig. 1comprising line finder 23, dial pulse forming circuit 24, dial register25 and line selector circuit 26 may be considered together as a linkcircuit. For certain embodiments of the system, a synchronizingfrequency may be fed from common equipment 22 over lead 29 to lineselector circuit 26 and line finder circuit 23 respectively. The fiveleads 2'5, 23, 29, 36 and 31 to and from common equipment 22 may also bemultiplied to other link circuits of the system as shown.

The distributor function of common equipment 22 may be performed by arotating distributor in the form of a cathode ray tube as illustrated indetail in Figs. 2 and 3. The distributor tube is indicated generally at39 and may comprise a cathode 40, the usual grid 4!, focus and anodeelectrode 42, horizontal deflector plates 43 and vertical deflectorplates 44. Two-phase distributor currents from a suitable sweep controlmay be applied over leads 45, 46, 41 and 48 to the horizontal andvertical deflector plates respectively, so as to produce a cyclicrotation of the electron beam. At the target end of tube 39 are providedtwenty coupling targets 49 to 68, respectively, which are coupled withthe individual lines I to 28 inclusive. These targets may comprisesecondary electron emissive elements associated with a common anode 69to provide dynodes all having a common output. A mask or screen 10 maybe provided, if desired, having apertures therein so that the electronbeam will impinge on each dynode only when the beam is aligned therewiththus preventing possible secondary emission from others. The output ofthe distributor tube 39 is connected from anode 69 over lead H, thensignal isolating circuits hereafter described to leads 2's and 28 whichgo to the line finder circuit as shown in Fig. 1. The output from theline selecting circuit 26 may be applied as indicated over line 36 tothe grid 4| serving to modulate the beam in accordance with the selectedsignal energy. Thus, referring to Fig.

1, the output from lead ll may be applied after suitable delay (producedin line selecting equipment 26 as hereafter described) over lead 36 togrid M to provide the desired communication channel between the chosenpair of lines.

v The common equipment 22 is illustrated in Fig. 4. For illustrativepurposes a base frequency of 10,000 cycles per second has been selectedas the scanning rate of the rotating distributor. This frequency issulficiently high to reproduce voice frequencies with adequate fidelityfor transmission of speech. For the twenty-line system the basefrequency is derived from a 200 kilocycle stable oscillator 12preferably crystal controlled. This higher frequency is preferablyutilized since it is generally easier to build a more stable oscillatorat the higher frequencies than at the lower 10,000 cycle frequency whichis to be used. Furthermore, in certain of the modifications illustrated,the 200 kilocycle wave may be utilized for other control purposes. Thesinusoidal frequency generated in master oscillator 12 is reduced to thebase frequency of ten kilocycles in frequency divider I3.

The output of frequency divider 13 is applied over 90 phase shifter 14to the vertical and horizontal sets of deflecting plates 43 and 44 ofdistributor tube 39 herein diagrammatically illustrated. This will serveto rotate the beam at a frequency of 10,000 revolutions per second sothat each of the dynodes 49 to 68, illustrated in Figs. 2 and 3 and inthis figure, will be scanned once every 10,000 of a second. Incominglines I, 5 and are shown connected to the respective dynodes 49, 53 and68.

At 2| is illustrated a typical subscribersubset (shown connected to line5) for use in the system according to my invention. Such a subset willbe connected to each of the incoming lines I to 20 inclusive. The voicetransmitter 15 is connected in series with dial I6 and the normally openswitch hook Ti. The receiver 18 is bridged permanently across the line,since, for simplicity of illustration, no separate ringing equipment hasbeen illustrated. Accordingly, the signal for summoning a calledsubscriber may be applied as a special tone which will be reproduced inreceiver 18 to call the listener to the phone. I

As in the usual equipment, switch hook 11 is normally open. However,upon initiating a call, the switch becomes closed, completing a circuitin the calling line loop over low-pass filter l9 and the associatedlines at the sub-set, applying a negative potential from battery 80 tothe associated dynode 53. Normally the dynode electrodes '49 to 68 areat the same potential as anode 69 so no current flows. This negativepotential will produce a difference in potential and cause secondaryemission current to flow from the dy nodes upon impingement of the beamof tube 39 thereon, producing a negative output pulse in output line H.The pulses are preferably signal modulated to a depth of only to 50 percent so that there will always be sufficient amplitude to furnish energyto establish and maintain connections regardless of modulating signals.The negative pulses resulting from operation of the selected dynode 53are fed to the grid of inverter tube 8|. The anode circuit of tube 8| iscoupled to the grid of clipper tube 82 which serves to clip these pulsesat a predetermined level to pass only the modulated portions of theincoming pulses. Thus, the output of this tube, representing the speechsignals, may be substantially 100 per cent 6 i modulated. These clippedpulses are then ap plied to a cathode follower tube 83 and from there toall of the link circuits over the cathode follower output lead 28. Asecond output is taken across the cathode resistance of inverter tube8|, these pulses being applied to a clipper tube E l which serves toclip the pulses to a constant level eliminating modulation effectstherefrom. The anode circuit of tube 84 is coupled to the grid of acathode follower tube 85 which serves to apply pulses 88 through commonfeed resistor 81 over wire 27 to the grid of line finder gate tube 88(shown in Fig. 6) of line finder 23 (shown in Figs. 6 and l) in thefirst link circuit (now under consideration) and in parallel to thegrids of the corresponding line finder gate tubes in all other links.The pulse 86 after passing through resistor 8"! may be called 89, sothat the pulse actually arriving at the grid of tube 38 and of the othersimilar tubes is pulse 89. Under the conditions now assumed, when noneof the grids of the line finder gate tubes is drawing grid current,pulse 89 is nearly as strong as pulse 86; but under other conditions itmay be much weaker than 86 as hereafter explained. In the absence of anysignals on the cathode of this line finder gate tube 88, the abovetraced pulse 89 on its grid is insufficient to cause the flow of platecurrent, because the bias applied to the grid is sufficiently far belowcutoff.

In the line finder 23 (Figs. 1 and 6) is provided an oscillator 90normally operating at a frequency slightly lower than the outputfrequency from frequency divider 13 in Fig. 4. This oscillator may, forexample, operate at one-fiftieth of one per cent below the frequency ofthe frequency divider. The output energy from oscillator 98 is appliedto a clipper amplifier 9! which serves to produce rectangular selectingpulses fifia. These pulses are differentiated in a differentiatingnetwork consisting of condenser 92 and resistor 93, to produce the pulseformation 94 which is applied to the control grid of clipper tube 95.The output pulses 96 from tube 35 (corresponding to the leading edge ofpulse 90a and the positive part of formation 94) are applied to cathodefollower tube 91. The resulting pulses 98 are applied to the cathode oftube 88 normally tending to make the cathode of this tube more negativeso that the tube will be more nearly conductive. However, except whenthe pulses 98 applied to the cathodeof tube 88 coincide with thepreviously traced incoming pulses 39, applied via wire 2? to the gridthereof, tube 88 is ineffective. Sufiicient bias is applied to the gridof tube 88 from battery 99 so that it requires the combined amplitudesof the two pulses 89 and 98 to operate this tube. As oscillator 96continues to drift relative to the output of frequency divider E3, thepulses 98 will commence to coincide with the pulses 89 incoming from thecalling line, overcoming the bias in tube 88 and producing output pulsesI00 in line 32. These output pulses I00 then are applied over condenserHill to a peaked amplifier and phase corrector circuit H12 which servesto lock oscillator 99 into step with the incoming pulses 89 so that itsoutput is in synchronism with the frequency from divider l3, and pulses98 will then continue to coincide regularly withthe incoming pulses 89from the predetermined calling line. As soon as the oscillator is lockedinto step, the pulses from line 32 also are applied over rectifier I03and an integrating network HJE- to a control grid of delayed gaincontrol tube 105. Operation of tube increases the positive voltage onthe screen of clipper tube 95 increasing the amplitude of the outputpulses 95 and hence 98. The value of resistor 81 and the grid. currentcharacteristics of tube 38 are such that the total positive swing of itsgrid with respect to its cathode cannot exceed a predetermined smallamplitude regardless of the magnitudes of pulses {I8 and 86 which areapplied respectively to the cathode and via resistor 81 to the grid oftube 88. However, the square pulses 98 from tube 97 will increase inamplitude with the change in bias of tube 95. Thus, since the sum ofpulses 89 and 98 is roughly constant, while the value of the component98 is rising, it is clear that the magnitude of pulses 89 must be.corespondingly decreasing. This decrease in amplitude of pulse 39 isefiective to prevent other line finder gate tubes (similar to 88 but inother links) from responding as more fully explained hereafter inconjunction with Fig. 10.

This decrease in pulse 89 does not, however, reduce the response of tube88 in the first link (now under consideration) since the totalrinputbetween grid and cathode is not decreased. Thus, pulses I89 are roughlyconstant in amplitude. These pulses iIlIl from the line finder gate tube88 are applied also over line 32 and coupling circuit I66 to gatecontrol tube IIl'I which serves to control the suppressor bias on theinput gate tube H38. Tube I53 is normally conditioned by suppressor gridbias so that the pulses applied thereto from the output of cathodefollower 83 over line 28 will not be passed by the tube. However, uponoperation of tube ,I e1, by selection of a predeterinhied incoming lineas described above, the suppressor grid of tube I08 has applied to itsuch a potential that the tube becomes conductive during the instantscorresponding to the time-channel of such predetermined line.Accordingly then, combined dial-and-speech pulses I09 will be appliedfrom the output of tube I08 over line 33 to the pulse forming equipment26 of Figs. 1 and 5 and to the line selecting equipment 26 of Figs. 1and 8. However, the energy applied to the line selecting equipment ofFig. 8 will not be passed until such time as line selection has beeneffected which will be described later.

Line finder 23 having now operated, pulses I89 from line 33corresponding to the time channel individual to the predetermined lineassumed to be calling are applied to an integrating network I I5 whichmay or may not be preceded by a pulse stretching circuit similar to apeak voltmeter. These pulses are then amplified in tube III and areapplied over transformer II2 to the control grid of the clipper tube II3and to the control grid of a second tube I'M. The integrating network H5in the input circuit of tube III func tions as a low-pass filter whichwill pass the dial pulses but will not pass the higher frequencycommunication signals. The clipper H3 serves to shape and clip theincoming dial pulses to form square wave pulses H5 which in turn aredifferentiated in network H6 and applied to the control grid of dialgate tube I II. Tube II! is biased so as to suppress the negative partof the difierentiated pulse (corresponding to the leading edge oi thesquare dial pulse I I5) and to pass only the positive part of thedifferentiated pulse, corresponding to the trailing edge of such squarewave pulse I I5. Normally tube I I1 is nearly cut-ofi by the voltagedrop in its screen grid resistor III! which is common with the plate ofa normally conducting tube IE9 of a flip-flop circuit which operates inconjunction with tube I I4. Time constants of this circuit are soadjusted that theleading edge of the first dial pulse serves to causetube I I4 to operate, cutting oif tube I I9. Low-pass filter I23 inthegrid circuit of tube I I9 causes this condition to be maintained untilafter the last pulse has passed, when the flip-flop circuit will returnto normal, again rendering the dial gate tube. I I! insensitive. Byprovision of this special blocking circuit, transient effects before andafter dialing will not affect the register. The output pulses from dialgate tube II! are applied over line 35 to the dial pulse registercircuits 25 of Fig. 1, this pulse passing through resistors I2I and I22to grids of the first register stage.

The dial pulse register circuits consist of a series of tubes of whichI23, IZ I, I25 and I26 are shown in detail connected as conventionaltrigger circuits for operation as a binary counter. Blocks I2'I, I28 andI29 constitute further register trigger circuits not shown in detail,there beinga sufficient number of these register circuits to count anydialing number in the exchange. With the system shown for twenty linesthe five shown are sufiicient. Initially, the tubes on the right handside such as I24 and I25 are conducting serving to bias tubes I 23 andI25 to cut-off. Furthermore, voltages developed in the register circuitsare applied as will be described later in more detail over lines MEL-I39to bias the various delay gate tubes to cut-off and the zero gate tubesto conduction in the line selecting circuit of Fig. 8.

The negative pulses incoming over line 35 are applied to the firstregister circuit including tubes I23 and I2 1. When the register circuitis in its normal condition, that is with tube I24 conducting and tubeI23 biased to cut-off, voltage is applied. to line I36 maintaining theassociated zero device of Fig. 8 in operation and over line I3I blockinga delay gate to be described in more detail later. The first incomingpulse on line 35 passes through resistance I2I to the grid of tube I24thus causing this tube to cut-oif rendering, however, tube I23 operativeand app-lying control voltages to lines I30 and I3I which serve to blockthe first Zero gate and open the first delay gate. The output from tubeI24 is applied over a line I to the second register circuit comprisingtubes I25 and I25 serving to transfer conduction from tube I25 to I25and from I25 to I26 alternately each time the trigger circuit I23, I24restores to normal condition (i. e. each time tube I24 becomesconductive). It will thus be clear that the second register shifts itscondition for every second pulse applied to the first register whilethefirst register changes its condition for every incoming pulse. Thethird register I2: is similarly controlled over line I II' so that theregister circuit I21 changes its condition each time the second registercircuit restores to normal (i. e. each time tube I26 becomes conductive)making register I21 shift its condition once for every two operations ofthe second register circuit. The fourth register I28 is similarly causedto shift its condition each time the third register I2! restores tonormal and the fifth register I29 is similarly controlled from theoutput of the fourth register I28.

Turning now more specifically to Fig. 8, the operation of these variousregisters for controlling the delay will be more .fully explained. Inorder to understand the operation of this system it first should beunderstood that the dials such as It, Fig. 4, for each line are numberedwith digits from 1 to 2!) representing the twenty lines. Each dial forany particular line is set so that when a called line is dialed, anumber of pulses corresponding to the difierence between the callingline and the called line will be transmitted to the exchange. It thusbecomes necessary to produce time displacements in the communicationener y corresponding to the difference in timing between the scanning ofthe two line in the cathode ray scanning circuit 39. The difierencesignalling pulses operate through the pulse register circuit of Fig. 7as described above, to select the desired time displacement inaccordance with the line which is being called. To this end, each of theregister circuits is provided with a zero gate I42, I43, I44, I45 and M6associated with the first, second, third, fourth and fifth registercircuits respectively. Likewise, associated with each of theserespective registers are different delay gates I48 microseconds for thetwenty line system), I 49 (10 microseconds), I55 (20 microseconds), ISI(40 microseconds) and I52 (80 microseconds). Each of these delay gatesincludes a delay line. In the output of each of these delay lines aredelay gate tubes I53 and I56 being illustrated in the case of gates I48and I 49. It is understood that similar delay lines and gate tubes areprovided for the other delay gate circuits. In the normal condition,before any pulse arrives, the system is biased so that the zero gatesI42 to I55 are all operative so that no delay will be provided in any ofthe pulses I I39 incoming over line 33 from the line finder circuit ofFig. 6. These pulses I09 therefore will be applied directly from line 33through the zero gate circuits I52 to I 35 inclusive, and from thereover line I55 to the output gate tube I56. Assuming for the moment thattube I56 is not disabled, its plate delivers corresponding pulses I51over line 35 to the control electrode of tube 39, Fig. 4, and thenceback onto the calling line. The first time the first register operates,the control potential is transferred from line I35 to line I3I renderingtube I53 conductive and biasing tube I42 to cut-01f. Thus, if one pulseonly is dialed, a delay of five microseconds is produced so that theenergy incoming over line 33 will pas through the first delay gate I43and the remaining zero gates I43 to I46 inclusive. The second pulsetransfers the control potential from line I3I back to I30 causing zerogate I42 again to become operative and blocking tube I53 in delay gateI48. At the same time, the second register operates transferring .thepotential from line I32 to line I33 blocking the second zero gate I43and opening gate tube I54 in the second delay gate I 59 introducing aten microsecond delay between line 33 and line I55. Thus, the secondpulse will produce zero delay in I42 ten microsecond delay in I59 andzero delays in I55 to I46. The third incoming pulse will not affect thesecond register circuit but will again operate the first registercircuit introducing the five microsecond delay gate I58 as well as theten microsecond delay gate Hi9 producing a fifteen microsecond delay inthe incoming energy. The fourth pulse then will return both the firstand second register to normal but will operate the third register I2!producing a twenty microsecond delay at delay gate I561. The fifth pulsewill again insert the five microsecond delay gate Hi8 so that there willbe five and twenty microsecond delays producing a total of twenty fivemicroseconds. The next pulse will switch out the five microsecond delayline and switch in the ten microsecond delay line producing a totaldelay of thirty microseconds. The next pulse will switch in the fivemicrosecond W delay line while leaving the ten and twenty microseconddelay ineffective thus producing thirty five microsecond delay. The nextsuccessive pulse will then render delay lines I 38, M9 and I55inefiective but will bring into circuit the fourth delay gate I5I withits forty microsecond delay. The other pulses will then bring in, insimilar sequence, the five, ten and twenty microsecond delay gates I 48,I59 and I55 introducing in sequence five microsecond delays until delaygate I52 is operated whereupon the process will again be repeated infive microsecond steps. Thus, with the five delay gates it is Possibleto produce any desired delay condition in the twenty lines. It will beclear that if a different number of lines are provided, additionalstages for the binary counting system and additional zero gates anddelay gates similar to those outlined herein may be provided to securethe proper delay in interconnection for any number of lines.

After the desired number has been dialed, the signalling energy from thecalling subscriber will be transmitted as described over the commonequipment circuit and line 33 in the link circuit the control electrodeof tube 39 as illustrated.

The voice modulations of pulses I57 incoming over line 36 will thenproduce variations in the electron stream of tube 39 each time the beamis aligned with the called line electrode and this variation in energywill be passed over the line to the corresponding low-pass filter IQ ofthe called subscriber to the receiver circuit I8. For the purpose ofcalling, a tone frequency may be transmitted to operate any suitabletone control apparatus at the called subscriber's line or the output ofreceiver '18 may be such that attention is directed to the phonedirectly by whistle or other call transmitted by the calling subscriber.

In the foregoing it has been assumed that tube I55 was conducting, forthe purpose of simplicity of explanation. Actually this tube is normallybiased to cut-off in order that the dialing pulses incoming over linecircuit 23 do not afiect other lines during the dialing. This cut-offbias of output gate tube I56 is controlled by the gate control circuitcomprising tubes I55 and I59. Tube I58 is normally conductingmaintaining the grid of tube I55 biased to cut-off. These tubes I 58,I59 in turn are controlled by tube I I9 as follows: As explained abovetube H9 of Fig. 5 becomes cut-off at the beginning of a series of dialpulses. At such time it sends out an inefiective positive pulse throughcondenser I65 to the grid of tube I58. As soon as the dialing operationis complete, however, tube H5 returns to conducting condition sendingout a negative pulse. This negative pulse cuts off tube I58, which inturn renders tube I59, and also gate tube I55, conductive. This permitsthe message energy to be transferred over line 35 to the calledsubscribers line.

In order to protect the called line from being seized by the linefinders of other links when the called subscribers receiver is removedfrom the hook, a portion of the delayed pulse I5? is tapped from line 35over line 3'! through isolating resistors I5I in Fig. 4 to a busy pulseshaper I 52 from whence it is conducted to the grid of busy gate tubeI65. This limits the maximum possible value of the positive line finderpulse from tube 85 which will be applied, after the called subscriberraises his receiver, to a value which is insufficient to operate theline finder gate tube of a searching line finder.

When the. call is completed and the calling subscriber hangs up, theregister circuits of Fig. 7 and the output gate control, I58 and I59 ofFig. 5 must be restored to normal. This is done with tubes I64, I65 andI85 of Fig. 7. When the line finder 23 locks in, tube I55, Fig. 6 isdriven to cut-ofi lowering the potential on the grid of tube I64 overline 5|. This causes the flip-flop circuit comprising tubes I54 and I55to operate transferring the conduction totube I55. A negative pulse isthus sent over line I5? and condenser I58 to tube I66 which is biased tocut-off and, therefore, has no effect. Now when the line finder releasesdue to the Calling subscriber hanging up, tube I05, Fig. 6, againconducts raising the bias on tube 564 over line 3! causing the flipflopcircuit I54, I55 to return to normal. The return of this circuit tonormal sends a positive pulse to tube I59 lowering the potential oncommon resistance I59, thus restoring all of the re ister circuits andoutput gate control tubes I58, I59 to norm-a1. In order to avoidexcessive interaction between various register circuits and output gatetubes, resistor I59 should be sufficiently low. Then to insureresetting, tube I65 should carry sufiiciently high currents. This tubemay comprise several tubes in parallel.

In order to explain the operation of the system, a call will be tracedthrough the circuit from line I to line 5. When the calling subscriberon line I removes the receiver from the hook in his sub-set (not shown)negative potential is applied to the dynode electrode 59. When the beamof tube 39 next traverses contact 59, secondary emission from thiscontact will produce a pulse in the common anode 55. This pulse thentraverses through inverter circuit 5!, clipper amplifier 85, cathodefollower 85, resistor 8? and line 21 to the line finder gate tube 88.Line finder gate tube 88 then produces output pulses I55 which serve tolock oscillator 9E3 into place with the calling line. Thereafter, thepulses 95 derived from this oscillator (and therefore also the reshapedpulses 98) are maintained in coincidence with input pulses 89. Becauseof this coincidence, only that set of pulses 89 corresponding to thetime channel of the calling line now under consideration are passed aspulses Hit by the gate tube 88. All other pulses 89 correspond ing totime channels of other calling or called lines are suppressed, thusselecting exclusively the pulses of the line under consideration. Theseselected pulses I then serve to operate gate control tube It! renderinginput gate I98 next conductive, at the correct instants. The outputpulses I09 from this tube I08 also represent only the desired ones ofall the pulses received from anode 59.

I The calling subscriber now dials the number which in thisinstanceproduces four successive reductions of the bias on dynode 49.The result is that the particular set of pulses arriving over line H asa result of the scanning of this dynode suffer four successivereductions in amplitude. These pulses are applied over line H, platecircuit of inverter BI, clipper tube 82, cathode follower 83, line 28 tothe control grid of input gate I08. Because of the action of clippertube 82, the four reductions in amplitude of the set of pulses nowappear as four complete breaks in this set of pulses. These incomingpulses with their four dialing breaks then are repeated through tube I88to line 33 as pulses I 09. The pulses I09 are transferred overintegrating network Ilii where the dialing breaks 12 are changed todialing signals. These dialing signals pass through amplifier III,transformer I I2, clipper H3 (where they become square wave H5). Thesepass through differentiating network H6, dial gate tube II! and line 35to the register circuit. Simultaneously, the dialing signals passthrough the further integrating circuit I20 to trigger the delay gatemechanism comprising tubes I M and I I9 into abnormal condition (i. e.with H4 operative and H9 cut-off) and this mechanism increases thepositive screen bias of dial gate tube III so that it will readily passthe pulses H5 derived from these dialing signals. The successive pulsesH5 then control the first three registers so as to bring the third oneto abnormal condition but to restore the first two back to normal. Thisinserts delay gate I50 into circuit producing a twenty microsecond delayequivalent to the time difference in a cycle of the beam sweep ofdistributor tube 39 between terminal 4-9 and output terminal 53associated with line 5. Simultaneously, the increase in plate potentialof tube H9 applies a positive pulse through condenser I55 to gatecontrol I58 and I59; but this has no effect, leaving tube i58conducting, thus maintaining output gate tube I56 blocked during thedialing interval. As soon as the dialing is completed, the positivepotential is removed from the grid of tube H4 restoring delay gatemechanisms H4, H9 to its normal condition with tube I I9 conducting.This reduces the screen bias of tube HI preventing further signals fromreaching the registers of Fig. '7. Simultaneously the decrease of platepotential of tube I I9 sends a negative pulse through condenser I65 togate control I58, I59, triggering this to its abnormal condition withtube I59 conducting. This unblocks output gate I56. The voice signalpulses I55 arriving over line 33 are applied to the output gate tubeE56. This tube then delivers output pulses I51 over line 36 to controlgrid 35 of tube 39 causing the beam to be modulated in amplitude inaccordance with the signals incoming over line I each time the beam isin contact with the electrode 53 corresponding to line 5. These pulsesvarying in amplitude in accordance with the voice signals are thentransferred over the corresponding lowpass filter 19 to the receiver I8of the called subscriber.

When the calling subscriber completes the call and hangs up hisreceiver, the calling loop circuit is opened and the negative potentialremoved from electrode 49. When the beam then sweeps past 49 no outputpulses will be applied over line II and connections to the line findercircuit will be broken. At the same time, the connection to the linefinder circuit is broken, the output from the delay gain tube I55terminates, and the control of lock-in oscillator terminates so that theline finder is again free to pick up any new incoming call. At the sametime, the potential from tube I55 is applied over line 3| to the releasetube circuit I64, I85. Release tubes I64 and I55 restore to normal withIE4 conducting. This produces a positive pulse which is transmittedthrough condenser I68 to tube I66. This applies a restoring potential tothe common resistor I59 restoring all the register circuits to normal sothat only the zero delay gates I42 to we are again operative. Similarly,gate control i58, IE9; is restored to normal with tube I58 conducting.Thus, the whole link circuit is restored to normal.

In order that the pulses from any one incoming line may be eifectivelyreduced in amplitude so as to prevent other line finders from thereafterI seizing the same calling line I, the delayed gain tube I85 andassociated circuit are provided. It

will be clear from the above description that when two or moresubscribers are using the exchange at the same time there will be aplurality of differently timed pulses in the line circuits of the commonequipment of Fig. 4. These pulses from the output of cathode follower 83are applied to all of the link circuits in parallel. When one linkcircuit, however, has taken hold it is necessary that the pulses of thisselected circuit be made ineffective to seize other links. A betterunderstanding of the operation of the system to prevent this operationmay be had by reference to Figs. 4 and 6 and the curves illustrated inFig. 10.

The pulses from the rnode 69 of tube 39 are applied to the grid of tube8I which has separate plate and cathode outputs. The pulses from theplate output of tube 8I varying in amplitude in accordance with anincoming signal are shown in curve IOA. These pulses are clipped inclipper 82 at the level I10 so that only the modulated or varyingamplitude portions ll! of the pulses are passed out through the platecircuit of this tube to cathode follower 83. Preferably, the energy isonly about modulated so that the modula- U tion variations willconstitute the minor portion of the pulsing energy. These pulses areused for transmitting speech and are not of interest in connection withthe feature now being considered.

The pulses from the cathode output of tube 8! are the ones of primaryinterest. These pulses are clipped in tube 84 and passed through cathodefollower 85 so as to produce a series of equal amplitude pulses 86 asshown in curve lIlB. These pulses 86 are applied through resistors 8'!as pulses 89 to the grids of all line finder gate tubes 88 in Fig. 6.Lock-in oscillator 98 produces an output wave I12, curve IIlC, whoseperiod is slightly longer than the time interval between two pulses 89.Wave I72 is clipped at clipping levels I13 and I'M then differentiatedand again clipped to produce pulses whose leading edges substantiallycoincide with the instant of rise of wave I12 between the clippinglevels. These pulses which are preferably substantially wider than theincoming pulses 89, pass through cathode follower 91 and the resultingpulses 98 are applied to the gate tube 88. Since the frequencies areslightly different, the phase or time position of pulses 89 willcontinually shift with respect .to pulses 98 until pulse 89 coincideswith pulse 98 as shown in curve I9D. When this occurs, the line findergate 88, Fig. 6, is operated so that the pulses may pass through peakedamplifier I02 to the oscillator 96 looking it into step with the pulses.The phase correction of peaked amplifier I62 is so adjusted that sinewave I12 will rise through zero slightly before the time of arrival ofpulse 89. The pulses 98 will then be produced in fixed timerelationshipwith pulses 89 as shown in first waveform of curve IBE. Oncethese pulses are synchronized, the delay gain tube I85 cuts offincreasing the screen bias of tube 95 so that the selecting pulses 98increase from their normal "search amplitude to a much higher holdingamplitude as shown in the second waveform in curve IIlE, thus reducingthe effective height of pulses 89. Thus, pulses 89, applied to the gridsof line finder gate tubes (corresponding to tube 88) in all other linefinders will be very small as shown in the third waveform of curve IUE.Then even if coincidence between these pulses 89 and the normal orsearch selecting pulse 98 of such other line finders does occur, nosignal will be passed through the gate tubes of such other line findersas shown in the fourth waveform of curve IOE.

When the called party answers, the closure of his line loop 5 places onthe dynode 53 a potential similar to that of a calling line. If nospecial precautions were taken this would cause another line finder toseize the called partys line thus tying up an additional link. To avoidthis, the busy shaper I62, and busy gate I63 are provided which functionas follows:

After the completion of dialing the output gate, tube I56 commences topass the speech pulses I 57 over line 36 to control grid 35 ofdistributor tube 39 as previously described. Part of the energy of thesepulses I51 is branched from line 36 in Fig. 8 and passes over line 31and isolating resistor IE! to the busy gate shaper I82, which amplifies,clips and reshapes these pulses into strong, sharp constant amplitudepulses. (For this purpose the clipping level of speech clipper tube 82should be set so that the speech modulation never reduces pulses IIIbelow a small fixed minimum value.) The reshaped pulses from I62 areapplied to the grid of busy gate tube I63 to make this momentarilyhighly conductive. This gate tube I63 then imposes a fixed upper limitupon the amplitude of the positive pulses 89, so that these cannotattain an amplitude sufiicient to cause seizure of the called line byanother line finder. Preferably, however, this upper limit is, highenough to hold a line finder which has already locked itself to thecalled line (in order that the act of selecting a line already engagedas calling line in a previous connection shall not break down suchprevious connection).

Turning to Fig. 11, I have illustrated a delay line in the system wherethe longer delays are required. For the shorter intervals shown in delaygates I88, I89 and I58 of five, ten and twenty microseconds, artificialdelay lines of known form may readily be used. However, for the longerdelays, acoustic delay means may be preferable. The line may, forexample, comprise a container H5 filled with mercury I76, having alength where V is the velocity of sound in the liquid At the input endis provided a crystal, for example a quartz crystal Ill, in a suitablemounting ring I18, with an electrode I19 coupled with line Hill for theinput signal.

At the output side is provided a second crystal I8I mounted in asuitable ring I82 with an electrode I83 and coupled to an output lineI88. To take care of expansion of the liquid, an off-set portion I maybe provided with container I'i5.

As previously explained, amplifiers are provided with each delay gate sothat the net loss is the same as the associated zero gate.

The foregoing description covers a complete system. However, alternativestructures for use in the system may be provided, a few of which areshown in the other figures. Fig. 12, for example, shows an alternativearrangement of line finder and common equipment. According to thisarrangement, I have provided the same master oscillator '52, frequencydivider l3 and phaser for controlling the sweep of the beam in tube 39.A slightly modified form of coupling circuit for dividing the signal andsynchronized pulses is shown differing somewhat from that illustrated inFig. 4. The output negative pulse from distributor 59 if fed over line Hto an inverter I39 and then into two cathode followers iB'l, I88. Thetube L38 passes the speech signal to line 22- extending to all thelinks. This signal has not had its modulation depth increased since thisfunction is performed in the link circuits in this form. The controlsignal is clipped to constant amplitude in a sli htly different mannerwith a clamping circuit comprising duo diode I89 which limits theamplitude of the signal to the grid of the cathode follower 81. Thiscathode follower feeds through a series resistance 81 to the grids ofall the link circuit tubes 88, explained before.

These tubes are normally biased sufiiciently beyond cut-off so thatsignals 8% alone on the input electrode will produce no change in theoutput and as before, coincidence with signals 98 derived from the localoscillator is necessary to produce any response. Instead of providing alocal oscillator tuned slightly off the ten kilocycle range, I providein this system a local oscillator Iilil operating at two hundredkilocycles +-.1%. The output pulses 89 from the tube I8? are applied tothe grid of signal gate tube 99 While the output from oscillator his isapplied through two frequency dividing multivibrators l9! and 92 toprovide the desired pulses 96 which operate through tubes as and 9" toapply a selecting signal 98 to the cathode of this same tube 88. Therelationship between pulses 8i and 98 will progress as previouslydescribed until such time as selecting pulse 98 on cathode of tube 88 isapplied simultaneously with a control pulse 89 to the grid thereof.Thus, tube 88 passes a pulse E98 through to the grid of tube I93 of adelay flip-flop circuit comprising tubes 593 and 599, thus triggeringthis flip-flop circuit to its abnormal condition with tube 94conducting, sending to shaper I95 an abrupt voltage rise. This delayflip-flop circuit has a period of action adjusted by the constants ofthe grid circuit of tube I93. When it spontaneously returns to normal,the voltage to the shaper I95 drops back abruptly thus completing a longpositive pulse to the shaper. The pulse shaper serves to diiferentiatethis pulse and suppress the leading portion, the trailing portion ofwhich has a desired delay. This trailing portion is then amplified andapplied to oscillator i813 to synchronize it with the master oscillator'52. The halting of the relative drift of these two oscillators stopsthe pulse progression of pulse 88 with respect to 89 and serves to lockthe line finder to the selected line as previously described. Uponlooking into step, the pulses i570 from tube 88 are rectified inrectifier I83 serving to cut-off tube I increasing the gain of tube 95and hence the amplitude of the pulses 95 and then 98 which are appliedto the cathode of tube 88. Because of the fact that a higher frequencyis used for the local oscillator, a more stable operation and preciselock-in can be obtained.

The busy gate tubes I98 and I9? operate as before to impose upon thepulses 89 an upper limit somewhat lower than the limit imposed byclamper I89. This new limit being high enough to hold a previouslyengaged line finder but low enough to prevent engaging a new one. Inperi; for Figs.v 7 and 8.

forming this function, tubes I98 and I91 act in a manner similar to duodiode clamper such as I89. At the instant .of arrival of a positivepulse from busy pulse shaper I02 upon the grid of tube I93 it becomeshighly conductive and thus acts as a diode to prevent wire 21 fromrising above the potential of its cathode. Tube I9! acts as a reverseclamper to discharge the negative potential which would remain at theend of such pulses.

A still different line finder circuit is illustrated in Fig. 13 whichmay be substituted for Fig. 6 (again in the grouping shown in Fig. 9).The line finder oscillator arrangement is substan tially similar to thatshown in Fig. 12. However, the lock-in oscillator I98 incidentallyperforms a frequency division and, moreover, is controlled through themedium of master'oscillator 12 instead of being controlled solely by theselected line pulses. The lock-in oscillator I98 operates at a frequencyslightly less than the two hun dred kilocycles, its 50 kc. output beingfed through a clipper differentiator circuit I99 to the ten kilocyclesynchronized multivibrator 200. The output of this multivibrator 200 isapplied through the differentiating nets 92 and 93 to tube 95 whichserves to form and amplify the pulses. Tube 95 is normally biased beyondcut-off but the leading edge of each square Wave output frommultivibrator 200 is of sufiicient strength to first drive the gridpositive on a portion of the square wave. A negative pulse 96 ofapproximately five microseconds is produced in the plate circuit. Acathode follower tube 91 passes the signal or control pulse 98 to thecathode of line finder tube 88. When the signal 89 on the grid of tube98 coincides with the above-described selecting pulse 98, the tube 88conducts and passes a pulse I00 to three places, namely to diodes I03and 2M and over wire 32 to the line selecting circuit (if this is of thetype shown in Fig. 16).

This pulse I00 is rectified in tube 20I and fed to an integratingnetwork 202. The negative potential from the integrator is amplified intube 203 reducing the potential in cathode resistor 204 which is commonto tube 203 and tube 205. The reduction of this potential renders tube205 conductive. Thus, this tube 205 now commences to pass the sine wavefrom master oscillator I2, which is continuously applied to the gridthereof over line 29. This amplified wave is then passed through phasecorrector circuit 208 serving to lock-in oscillator I98 with the masteroscillator 12., Accordingly, progression of selection is now stopped sothat the pulses 89 will pass through tube 88 to open line finder gatetube I08 at the correct instants, thus causing the latter to pass thedesired signal pulses from wire 28 to wire 33 in the manner previouslydescribed in connection with Figs. 4 to 9 inclusive.

Simultaneously, the application of pulses I00 to diode I03 actuatestubes I05 and 95 to prevent engagement of other line finders aspreviously described.

In the system previously described, the dial register circuit and theline selecting equipment of Figs. 7 and 8 are provided with the binarycounting system together with delay lines to achieve the desired timedisplacement of the incoming pulse signals. An alternative combinationof a pulse register circuit and associated line selection circuit isshown in Figs. 15 and 16 respectively, which may be substituted as aunit Also an alternative pulse

